1. Field of the Invention
This invention is directed to an article of manufacture and to a method. More specifically, this invention relates to a novel assay kit, particularly to a test kit employing an analyte test strip and a novel color comparator for the analyte. This kit includes a dry chemistry reagent system incorporated within a reaction zone of a bibulous medium (solid phase) of the test strip. The reagent system is specific for an analyte of interest. Such kits are useful in the detection of biological substances, i.e. glucose, cholesterol etc. and in the detection of environmental toxins.
2. Description of the Prior Art
Manual test kits are typically used for obtaining a qualitative or semi-quantitative assay value for an analyte, such as glucose, in a fluid sample. Representative test kits are available from the Ames division of Miles Laboratories (i.e. Bili-Labstix.RTM.). One simple, low-cost, disposable kit can typically include a test strip having one or more reaction zones containing substances which produce a definitive set of color values in such zone in the presence of detectable quantitives of a particular analyte. The kit includes also a color comparator having a plurality of different color fields arranged in a linear succession for comparison with the color of the reaction zone. The color of each field connotes a particular assay value of the analyte.
In the Bili-Labstix.RTM., the test site is wetted with a urine sample. Then, after a designated period of time, each urine impregnated reaction zone within the test site of the test strip, is held over the color fields of the color comparator and the user tries to match the color of the reaction zone to the closest color among the color fields. In some of the more cumbersome of these test kits the user must refer to a separate numerical chart which translates the color fields into meaningful assay values.
One problem which arises when comparing and matching the reaction zone color with a color field is that the color of the support or inert portion of the analyte strip, (which is associated with the bibulous medium containing the analyte specific reactants), is usually white or near white. Because the inert portion of the strip is in the viewers visual field, it can change or distort the appearance of the color of the reaction zone to the naked eye. Also, in many such tests, the color of the reaction zone changes with time, so that the color must be matched promptly and the assay value obtained and recorded before a further color change prevents accurate correlation with the analyte content of the sample.
The following patents are representative of the prior art colorimetric assay test kits and techniques: U.S. Pat. Nos. 3,894,845 to B. McDonald; 3,964,974 to D. Banauch et al; 4,042,329 to H. T. Hochstrasser; 4,275,031 to W. Fischer et al; 4,391,904 to D. J. Litwan et al; and 4,532,216 to J. Y. Wang. As is evident from a review of these references, all the systems disclosed therein suffer from at least one common failing; the inability to permit rapid and accurate correlation of the reaction zone color with the appropriate comparative value in the companion color index.